Different Voltage Between Phases - Normal?

[JasonPAtkins]

Hey guys,

I'm working on the electronics to my first windmill and have a question, hopefully someone knows off hand since it seems like everyone would have run into this issue.  When we wired the stator and gave it a test spin with the leads of the meter phase one and two, we get some AC voltage, say 28V.  When moving the test leads to phase one and three, spinning the same speed, we get a higher voltage, say 40V-ish.  I figured that was because phase one and three are further off phase of each other than phase one and two.

Now we have the rectifiers in place and the DC voltage coming out of the phase two rectifier is still lower than phase one or three.  The phase two DC output is about half the one or three output.  Is this a case where it should be lower, and when we tie the DC output of the three phases together it all averages out, or does it necessarily mean that the phase was wired incorrectly?  

This seems like it would be easier to verify if we had left the point that ties the three phases together in the stator exposed so we could check the phases independantly, but since we have to measure them in relation to one another, it's a little more complicated.  Am I thinking about this incorrectly, are we ok and this is how it's supposed to be, or does it mean a bad stator wiring job?

Thanks!

[ghurd]

Not normal.

You have 3 wires leaving the stator?

Test V AC from 1 to 2, 2 to 3, and 1 to 3.

Phase 1 and 3 are the same as 1 and 2, just in the other direction.

Some of you numbers are confusing to me.  Not sure what you mean by the voltage of phase 2, or what that voltage is referenced to.

G-

[Flux]

As you say it would have been infinitely easier if you had left the star point accessible . If you only have 3 leads then the ac voltage between any pair should be the same. I suspect you have reversed the starts and finishes of one phase or you may have a more complicated mess up in the coils of one phase.

It would probably save a lot of frustration if you can do a little minor surgery and get to the star point. If all voltages are equal in relation to the star then you have a reversed phase. If things are still not equal then you have problems in the coils of a phase or phases.

You have a problem and it needs sorting, it will not come out in the wash when you rectify it.

Flux

[Flux]

"Now we have the rectifiers in place and the DC voltage coming out of the phase two rectifier is still lower than phase one or three.  The phase two DC output is about half the one or three output.  Is this a case where it should be lower, and when we tie the DC output of the three phases together it all averages out, or does it necessarily mean that the phase was wired incorrectly?  "

To be honest I can't make any sense of this bit. If it is a 3 phase rectifier you will get the single phase mean of the highest with a contribution from the lower voltage.

I don't see how you can see what the individual dc voltages are if it is a conventional 3 phase rectifier. If you are doing some form of Jerry connection you can't have a star point.

You certainly have a winding fault but I can't follow what you are doing with the rectifiers.

Flux

[Ungrounded Lightning Rod]

Please tell us:

 - The number of coils.

 - How they're connected.  (Y?  Delta?  All 6 ends out for external configuration?)

 - What the (ac) voltage measurements are across each pair of output terminals at some common RPM.

[imsmooth]

One of your coils must be backwards.  If it were me, I would scrap it, make another, and double check the orientation of each coil before casting the next one.

[richhagen]

The voltages through any two coils when connected in star should be similar.  There may be a slight difference of about 5% due to imperfect coil/magnet placement or other irregularities, but if the difference is at 35% from the mean voltage between any two phases at the same rpm, then something is wrong.  It may be that you've flipped the start and end on one of the coils in one of the phases, or a coil seriously out of place(which should be obvious by inspection), a short in a coil, or some other anomoly.

If you had left the star point accessable, then you could check each phase individually, but if there is a problem in only one phase, you should have a good chance of figuring out which if the voltages between two of the three sets of contact are low compared to the third.  I would start looking at the phase in common between the two sets of connections with the lower voltage for the fault.  If you can identify the phase, you will then likely have to dig out the coil connections to test further.

Is this one going to Guinea Bissau?  

Have fun, Rich

[(unknown)]

By testing the voltage next time, you can first check the resistance bewteen each phase first:)